RFR: 8351666: [PPC64] Make non-volatile VectorRegisters available for C2 register allocation [v4]

[Richard Reingruber]

On Wed, 9 Apr 2025 22:02:11 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>> Also: why is it even necessary to define VSR0 - VSR31 if we don't use them (because they are aliases of the FP regs)? I assume they unnecessaryly enlarge RegMasks and the size of RegMasks is critical for memory consumtion.
>
> I've removed them. This makes sense. Thanks for your feedback! I'll take a closer look at the other comments when I find more time.

> BTW: You might use vector pair load/stores in `MachSpillCopyNode::implementation()` too.

Probably not load/stores for _pairs_ but better instructions like lxv and stxv.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23987#discussion_r2036687779